LOCATION SHOT - SIRIUS IV GONE TO THE DOGS?

From the TARDIS Data Core:
Sirius IV was a planet colonized by humans. By the year 2540, however, it had become a dominion planet within the Earth Empire. 

As a dominion, Sirius IV had great autonomy within the Empire; it dealt with Earth mostly as an equal. The Master once used this special status as a way to negotiate for the release of the Third Doctor and Jo Grant into his custody. By fabricating charges against them on Sirius IV, he was able to successfully argue that he had greater claim to the prisoners than Earth Security. (TV: "Frontier In Space")

For the greater Toobworld, Sirius IV must have been inhospitable for colonization by the other populated planet in the system, Parenthia.  The main sentient species of Parenthia are canine humanoids (as seen in an episode of 'Bewitched'.)  It's likely that the Parenthians, who had the capability for light-speed space travel by the 1960s in Earth time, did not have the technology for terra-forming.  Explorers from Earth must have had to conduct peace treaty negotiations with the resident species of that star system to gain control of that seemingly dead planet.  But the Parenthians probably will be getting their "taste" from any profits gained from Sirius IV.

"Frontier In Space" took place in 2540, so it's pozz'ble, just pozz'ble, that Sirius IV had been Parenthia in the past.  But somehow the sentient canine population had been wiped out by the time Earth space explorers had reached that sector of space.

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BCnU!